it would be uselfull at times if functions like glRotate can be changed to take radians
I don’t think this would enhance performance because the one multiplication it would save you per call to glRotate is small compared to the work done inside each call. So it is just a convenience for the programmer. But wouldn’t it be easier, instead of having to load a new glRotate function or call glEnable(GL_RADIAN_ANGLES_ARB), to just use a function or macro to do the conversion? For example:
#define RtoD(a) ((a)*(180.0/M_PI)) ... glRotate(RtoD(angle), 1.0, 0.0, 0.0)
IMO, it’s simpler to use only one unit for angles in OpenGL. If you work in radians, just remember to convert to degrees.